The control of unwanted immune responses is a critical issue in the treatment of diseases such as inflammation, autoimmune diseases, transplant rejection, allergic diseases, and some cancers. The activity of overly aggressive T cells can be controlled by immunosuppression or by the induction of immunological tolerance. Tolerance is defined as a state where the immune system is made unresponsive to an antigen, whereas immunosuppression, which decreases the immune response to antigens, usually requires the continued use of medication. In inflammation and autoimmune diseases, T cells play an essential role in the prolonged immune response to a certain stimulus. Current immunosuppressive regimes commonly involve the use of corticosteroid, cyclosporin or rapamycin, which block the transcription of IL-2, a key growth factor for T cells, or inhibit IL-2 dependent proliferation. However, a number of monoclonal antibodies that act as T cell-depleting agents (e.g. CD3, CD4, CD8), or as inhibitors of the cytokine signaling or the co-stimulatory pathways of T cells (e.g. CD25, B7-1, B7-2, CD152, CTLA4) have demonstrated effectiveness in reducing the incidence of rejection with limited side effects or toxicity. Some of these agents have been shown to have some degree of success in treating inflammatory and autoimmune diseases and in prolonging graft survival.
The myeloid receptor of the C-type lectin superfamily associated with DAP12 is Myeloid DAP12-associating Lectin-1 (MDL-1), a type II transmembrane protein (MDL-1 is also referred to as CLEC5a). MDL-1 was the first DAP12 associating molecule to be identified and cloned (Bakker et al. (1999) PNAS USA 96(17):9792-9796). It is expressed exclusively in myeloid cells (Bakker et al. (1999) PNAS U.S.A. 96:9792-9796) as well as on other myeloid cell types such as, neutrophils and dendritic cells. The presence of a negatively charged residue in the transmembrane domain of DAP12 precludes its cell surface expression in the absence of a partner receptor, such as MDL-1, which has a positively charged residue in its transmembrane domain. However, DAP12 alone is not sufficient for its expression and function at the cell surface. Thus, the combination of a DAP12-associating molecule, such as MDL-1, and DAP12 may account for transmitting a particular physiological signal via DAP12 (Nochi et al. (2003) Am. J. of Pathology 162:1191-1201).
MDL-1 has been found to possibly be the receptor for Dengue Virus on myeloid cells (see, e.g., Chen, et al. (2008) Nature 453:672-676). Recently, MDL-1 has been structurally characterized as a “C-type lectin-like” homodimeric molecule that is capable of conformational switching in the presence of Dengue Virus binding (see, e.g., Watson, et al. (2011) J. Biol. Chem. 286:24208-24218).
The present invention identifies a population of T lymphocyte cells that appear to express a protein involved in MDL-1 engagement and activation. The ligand appears to be a cell surface protein that may not directly interact with MDL-1, but rather involves a third protein. A sub-population of these cells also expresses IL-23 receptor (IL-23R). Upon activation by IL-23, these IL-23R+, MDL-1L+ expressing cells have been implicated in the progression of inflammation, in particular enthesopathy.
The non-viral binding partner of MDL-1, MDL-1 ligand (“MDL-1L”), is now identified as Galectin9 (“Gal9”). Galectin-9 (Gal-9) is a member of animal lectins that have an affinity to β-galactosides. Gal9 has been shown to bind to several other molecules, including T cell immunoglobulin and mucin domain-containing molecule (“TIM3”), which is expressed on Th1/Th17 cells, and is a negative regulator of Th1 immunity (see, e.g., Zhu, et al. (2005) Nat. Immunol. 6:1245-1252; and Jayaraman et al. (2010) J. Exp Med. 207:2343-2354). Gal9 has also been shown to bind to other cell surface molecules such as CD44 and IgE (Niki, et al. (2009) J. Biol. Chem. 284:32344-32352), as well as protein disulfide isomerase (see, e.g., Bi, et al. (2011) Proc. Natl. Acad. Sci. 108:10650-10655).
Engagement MDL-1 by the Gal9 results in the activation of myeloid lineage cells (e.g., macrophages, osteoclasts) via DAP12, resulting in tyrosine phosphorylation of DAP12 and induction of an innate immune pathway. Uncontrolled induction of this pathway can either lead to chronic inflammation or improper clearance of infectious microbes. Thus a need exists to control the Gal9/MDL-1 interaction. The present invention provides methods to regulate this protein-protein interaction and screens to isolate additional regulatory compositions which modulate with this interaction.